Method of and composition for lining plumbago crucibles



(No maelb' J; PEDDER. METHOD OF AND GOMPOS'ITION FOR LINING- PLUMBAGO GRUGIBLES. N0. 243,789.

Patented July 5, 1881.

N. mm MW. MD-C- UNITED STAT S PATE T OFFICE.

JOHN PEDDER, OF PITTSBURG, PENNSYLVANIA.

METHOD OF AND COMPOSITION FOR LlNlNG PLUMBAGO CRUCIBLES.

SPECIFICATION forming part of Letters Patent 1 \To. 243,789, dated July 5, 1881. Application filed June 8, 1881. (No model.)

To all whom it may concern: 7

Be it known that I, JOHN Pnnnna, of Pittsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Method of and Composition for Lining Plumbago (.lrueibles; and I do herebydeclare the following to be a full, clear, and exact description thereof, reference being had to the accompanying drawings, forming a part of this specification, in which- Figure 1 is a vertical section of a plumbago crucible, illustrating the condition of the crucible where rents or cracks are formed on its inner surface, and Fig. 2 is a like view of a crucible, in which in yim proved linin ghas been formed.

Like letters of reference indicate like parts in each. i

My invention relates to the protection of the inner surface of the plumbago crucibles employed in melting steel, brass, a nd other metals. These crucibles have generally been formed of plumbago and German clay, with a slight portion of silica, being known as plumbago crueibles. The crucibles are generally molded in a mold on a pottery-machine by means of a forming-tool, and are afterward dried and baked in a suitable kiln. ltsometimes occurs that the drying or baking of the crucible causes an undue shrinking of the crucible material, and hence a parting or renting of the inner walls, so that small cracks or rents are formed over the inner surface. 'In some cases also blisters are formed on the interior of the crucibles, and when broken they leave holes. As the molten metal enters thesecracks, rents, or blister-holes it forces its way through them, forming holes in the pot, through which the metal runs out, these pots being usually called runners. These cracked or blistered crucibles have, therefore, been considered unfit for use, and have been ground up to be molded into crucible-caps and like articles which do not require the same strength as a crucible. Where new pots also are used in the manufacture of steel and like metals the interior surface is eaten off by the molten metals and the fluxes used therewith, such as manganese and spiegeleisen, so as to wear into the body of the crucible, and in some cases, where a piece of clay, metal, or other foreign substance is molded in the pot, it will melt or burn out andleave a hole through which the metal will enter and form a runner.

The object of my invention is to utilize the cracked or blistered crucibles and prevent the molten metal from entering the cracks or blisters to penetrate the crucible, as well as to protect the inner surface of these imperfeotor of perfect crucibles from wear, and so enable the crucible to last longer than when unprotccted.

My invention consists, first, in protecting the cracks, rents, or blisters, as well as the interior surface of the crucible, as far as necessary, from contact with the molten metal by forming within the crucible, before use, a liningor case composed of plumbago, silica, and salt, or similar materials, and thoroughly drying out any moisture contained in the lining before the crucible is used and, second, in the composition used for lining theiuterior of the crucible.

To enable others skilled in the art to make and use my invention, I will describe it more fully.

In the drawings, Figure 1 represents a crucible of the usual construction, in which have been formed cracks or rents a and blisters b in drying or baking. These cracks or rents a are caused by the uneven shrinkage of the crucible material in drying before being placed in the kiln for baking, or during baking in the kiln. The uneven shrinkage causes the material to part, so forming the cracks or rents, which are sometimes scarcely perceptible, and in some cases open out over an eighth of an inch. These cracks or rents generally occur in the lower part of the crucible interior, and if any appear the pot is considered imperfect and is notused, as the cracks are almost certain to open out further in the melting-furnace and cause runners. The blisters b are generally formed by subjecting the pot to too high a heat, which causes the blister to rise in the crucible interior and leave a hole beneath it, into which the moltenmetal passes, gradually cutting through the pot. In these cracked or blistered crucibles, which were heretofore considered unfit for use, I form my improved lining or case (1, as shown in Fig. 2, thus fully protecting the cracks or other imperfections from contact with the metal, so that it cannot work through the pot. The inner surface of the perfect or marketable crucibles is eaten or cut off by the metals and fluxes, which wear out the interior very rapidly, and I also form this case (I in these crucibles to prevent this wear or cutting. My improved lining or case (I is generally formed of plumbago or groundup pots, silica, salt, and water in which a small portion of kaolin, German clay, or other suitable clay has been dissolved, this clay-water acting as a bond between the other ingredients to hold them together. The lining is preferably made by taking about twenty parts of plumbago or ground-u p pots,ten parts of silica, one part of salt, and suflicient clay-water to form a mortar that will run or flow around the cruciblevwhen placed therein. I

Instead of salt, a suitable analogous material which will unite with the silicate or silica to form a glaze may be employed.

The composition thus formed is placed in the bottom of the crucible, which is tilted over and gradually turned around, so as to enable the composition to run around the crucible interior, thus forming a case or lining from one-eighth to three-eighths of an inch thick. The lining is formed in the samemanner in perfect or marketable crucibles to protect their inner surface from contact with the metals and fluxes. The height of the lining in the crucible will depend upon the position of the cracks or blisters to be covered, or, where perfect crucibles are lined upon the surface desired to be protected, the height of the covering thus depending on the will oftheoperator. There the cracks or blisters are large a portion of the composition may be pressed into them before or during the lining of the crucible.

It has hitherto been the general understanding in the trade that plumbago crucibles must be preserved from dampness or contact with water before first subjected to theintense heat of the melting-furnace, it being supposed that any such contact would cause the crucible to scalp or crack. Though this is believed to be true as to the outer surface of. the crucible, l have demonstrated by actual practice that if the lining formed in the crucible, as above described, is thoroughly dried, so as to drive out all moisture before the crucible is used,the water of the lining-composition has no injurious effect on the crucible. For this reason, after the lining has been formed in the crucible, as above described, the crucible is then placed in a suitable drying-oven or over the melting-fun naces, and the water of the lining composition is entirely dried out by the heat, when it will leavea hard dry lining or case within the crucible. When the crucible is brought to the high heat necessary to melt steel and like metals the sodium of the salt unites with the silicate in the clay of the clay-water and the silica or sand of the lining-composition, and forms a flux or glaze which covers the surface of thelining or case. This glazedlining or case, after it is once formed, effectually prevents the metals from eating into the pot, and the manganese, spiegeleisen, or other fluxes from cutting through it, so thatthe inner surfaceof the pot is prevented from wear, whether in a perfoot orimperfectcrucible, and also prevents the molten metal from coming in contact with the cracks, rents, or blister-holes of the imperfect pot, so that as m uch metal can often be obtained from this pot so protected as from a perfect pot. Experience has also shown that the glaze formed as above described permits the carbon of the lining to pass through and unite with the oxygen of the metal in melting, which is very desirable in the manufacture of steel.

By the use of my invention the entire wear comes on the outer surface of the crucible, and

' consequently itlasts from three to four heats longer than where the metal and fluxes are allowed to cut into the unprotected inner walls. Imperfect crucibles which were heretoforeconsidered unfit for use are also so protected as to he often capable of the same use as the perfeet or marketable crucible.

\Vhat I claim as my invention, and desire to secure by Letters Patent, is-

l. The herein-described process of protecting the inner walls of plumbago crucibles, whether perfect or imperfect, consisting in forming within the crucible, before use in the melting-furnace, a case or lining composed of plum bago, silica, salt, and clay-water, or similar materials, and thoroughly drying out the moisture contained in the lining, substantially as and for the purposes set forth.

2. A composition for lining the interior of plumbago crucibles, containingplumbago, silica, salt, and clay-water, substantially as and for the purposes set forth.

In testimony whereof I, the said JOHN PED- DER, have hereunto set my hand.

JOHN PEDDER.

Witnesses:

JAMES I. KAY, F. G. KAY. 

